title: Electronic origin for the phase transition from amorphous Li(x)Si to crystalline Li15Si4.
abstract: Silicon has been widely explored as an anode material for lithium ion battery. Upon lithiation, silicon transforms to amorphous LixSi (a-LixSi) via electrochemical-driven solid-state amorphization. With increasing lithium concentration, a-LixSi transforms to crystalline Li15Si4 (c-Li15Si4). The mechanism of this crystallization process is not known. In this paper, we report the fundamental characteristics of the phase transition of a-LixSi to c-Li15Si4 using in situ scanning transmission electron microscopy, electron energy loss spectroscopy, and density function theory (DFT) calculation. We find that when the lithium concentration in a-LixSi reaches a critical value of x = 3.75, the a-Li3.75Si spontaneously and congruently transforms to c-Li15Si4 by a process that is solely controlled by the lithium concentration in the a-LixSi, involving neither large-scale atomic migration nor phase separation. DFT calculations indicate that c-Li15Si4 formation is favored over other possible crystalline phases due to the similarity in electronic structure with a-Li3.75Si.
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Meng
authors.initials: M
authors.lastname: Gu
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Wang
authors.forename: Justin G
authors.initials: JG
authors.lastname: Connell
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Perea
authors.forename: Lincoln J
authors.initials: LJ
authors.lastname: Lauhon
authors.forename: Fei
authors.initials: F
authors.lastname: Gao
authors.forename: Chongmin
authors.initials: C
authors.lastname: Wang
mesh_terms: D003198:Computer Simulation; D003460:Crystallization / Q000379:methods*; D004579:Electron Transport; D008094:Lithium / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D044367:Phase Transition; D012825:Silicon / Q000737:chemistry*
chemical_list: D008094:Lithium; D012825:Silicon